The present invention relates generally to rotors for DC or PM synchronous electric motors or synchronous alternators (hereafter referred to as generators) and, more specifically to a composite sleeve for such rotors.
A sleeve or a DC or PM synchronous motor/generator rotor serves several purposes. The rotor typically consists of magnets bonded to the outside diameter of a steel rotor hub on which there is a sleeve that prevents magnets from being thrown off the rotor and into the stator due to the centrifugal forces on the magnet caused by the rotation of the rotor. The sleeve also helps to protect the magnets from chipping during assembly.
Typically, such sleeves are hollow, substantially cylindrical, steel members which are interference fit over the magnets and hub. Steel sleeves increase the inertia of the rotor. The conductivity of a steel sleeve also undesirably facilitates the flow of eddy currents inside the motor.
It is an object of the present invention to provide a sleeve for a high performance DC motor rotor having only 20-27% of the inertia of a stainless steel sleeve, thereby increasing the acceleration rate of the rotor under a given torque.
It is a further object of the present invention to provide low electrical conductivity compared to a stainless steel sleeve, thereby reducing the flow of eddy currents in the sleeve.